Flowable tissue products

ABSTRACT

The present disclosure provides tissue fillers. The tissue fillers can include a plurality of tissue particles formed from acellular tissue matrix fragments. The tissue fillers can be used to fill tissue sites, such as voids formed after tissue resection.

This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 61/577,729, which was filed on Dec. 20, 2011.

The present disclosure relates to tissue products, and more particularly, particulate tissue products for use as tissue fillers.

Various tissue products have been produced to replace, augment, or treat tissue defects. For example, to replace or augment soft tissue defects, particulate acellular dermal matrices that form a paste or putty-like material can be used. Such products include, for example, CYMETRA®, which is a dermal acellular tissue matrix made by LIFECELL® Corporation (Branchburg, N.J.).

Although suitable for certain applications, further improvements in the ability of tissue products for soft or hard tissue treatment are desirable. The present disclosure describes improved tissue products produced from particulate tissue matrices.

SUMMARY

According to certain embodiments, a tissue product is provided. The product can include a plurality of dry tissue matrix particles comprising a longest dimension between about 1 mm and 5 mm. The tissue matrix particles can each comprise a plurality of tissue matrix fragments having a length between about 5 μm and 300 μm, wherein the tissue matrix fragments are formed into the tissue matrix particles.

According to certain embodiments, a method for producing a tissue treatment composition is provided. The method can include selecting a tissue matrix and treating the tissue matrix to produce fragments having a length between about 5 μm and 300 μm. The method can further include forming the fragments into a plurality of particles having a longest dimension between about 1 mm and about 5 mm; and treating the particles to join the fragments forming each particle to one another. In some embodiments, the present disclosure includes tissue products produced according to the disclosed methods.

According to certain embodiments, a method of treating a tissue site is provided. The method can comprise selecting a tissue site and selecting a tissue product, comprising a plurality of dry tissue particles, wherein the tissue matrix particles each comprise a plurality of tissue matrix fragments having a length between about 5 μm and 300 μm, and wherein the tissue matrix fragments are joined to one another to form the tissue matrix particles. The method can further comprise placing the plurality of tissue particles in or on the tissue site.

According to certain embodiments, a tissue product is provided. The tissue product can include plurality of dry tissue matrix particles that form a flowable mass that can be poured into a tissue site and will flow to fill and conform to a tissue site. The particles are substantially spherical and have a radius between about 1 mm and 5 mm. The tissue matrix particles each comprise a plurality of tissue matrix fragments having a length between about 5 μm and 300 μm, and the fragments are joined to one another to form the tissue matrix particles.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a process for producing a tissue product according to various embodiments.

DESCRIPTION OF CERTAIN EXEMPLARY EMBODIMENTS

Reference will now be made in detail to certain exemplary embodiments according to the present disclosure, certain examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

In this application, the use of the singular includes the plural unless specifically stated otherwise. In this application, the use of “or” means “and/or” unless stated otherwise. Furthermore, the use of the term “including”, as well as other forms, such as “includes” and “included”, is not limiting. Any range described herein will be understood to include the endpoints and all values between the endpoints.

The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described. All documents, or portions of documents, cited in this application, including but not limited to patents, patent applications, articles, books, and treatises, are hereby expressly incorporated by reference in their entirety for any purpose.

As used herein “tissue product” will refer to any human or animal tissue that contains extracellular matrix proteins. “Tissue products” can include intact tissue matrices, acellular or partially decellularized tissue matrices, decellularized tissue matrices that have been repopulated with exogenous cells, and/or cellular tissues that have been processed to change the orientation of at least some of the collagen fibers within the tissue's extracellular matrix.

Various tissue products are available for treatment of hard and soft tissues. Such tissue products can include processed tissues, which have been treated to remove some or all of the cellular components and/or other materials (e.g., antigens and lipids). Such tissue products can be used for treatment, repair, regeneration, and/or augmentation of a variety of different tissues. For example, acellular tissue matrices can be used to replace soft tissue lost or damaged due to, for example, surgery, trauma, disease, and/or atrophy.

Current tissue matrices or other tissue scaffold or replacements materials (e.g., processed collagen or synthetic materials) are available in a variety of different forms. For example, STRATTICE™ and ALLODERM® (LIFECELL® Corporation, Branchburg, N.J.) are two acellular dermal tissue matrix products that are sold as sheets. In addition, CYMETRA® (also from LIFECELL®) is a dry, particulate acellular dermal matrix, which is produced by cryofracturing acellular dermis. Each of these materials can be used to treat various anatomic sites. STRATTICE™ and ALLODERM® can be used for soft tissue augmentation, e.g., to treat abdominal wall defects; and CYMETRA® can be injected for soft tissue augmentation.

Although some currently available tissue matrices are suitable for treatment of certain anatomic sites, such materials may not be well suited for some applications. For example, when treating tissue defects of varying size and geometry, e.g., after surgical excision of diseased tissue, sheets may not be well suited to allow complete filling of a tissue site. In addition, particulate materials may be packed or placed into a tissue site (e.g., in the form of a paste or putty), but such materials may not flow adequately to fill small defects, and may not maintain sufficient porosity or space for rapid cellular infiltration and formation of vascular structures. Accordingly, the present disclosure provides tissue products that can be used to fill tissue defects having variable and/or irregular geometries. In addition, the tissue products of the present disclosure can provide suitable configurations to allow cellular ingrowth and vascular formation.

In various embodiments, a tissue product is provided. The tissue product can include a plurality of dry tissue matrix particles. The particles can be formed from tissue fragments that are joined to one another to produce the desired particle size and shape. In various embodiments, the particles comprise a longest dimension between about 1 mm and 5 mm and the tissue matrix fragments that form the particles comprise a length between about 5 μm and 300 μm.

In various embodiments, a method for producing a tissue treatment composition is provided. The method can include selecting a tissue matrix and treating the tissue matrix to produce fragments having a length between about 5 μm and 300 μm. The method can further comprise forming the fragments into a plurality of particles having a longest dimension between about 1 mm and about 5 mm.

In various embodiments, methods for treating a tissue site are provided. The methods can comprise selecting a tissue site and selecting a tissue product comprising a plurality of dry tissue particles, wherein the tissue matrix particles each comprise a plurality of tissue matrix fragments having a length between about 5 μm and 300 μm, and wherein the tissue matrix fragments are joined to one another to form the tissue matrix particles; and placing the plurality of tissue particles in or on the tissue site.

In various embodiments a tissue product is provided. The tissue product can comprise a plurality of dry tissue matrix particles that form a flowable mass that can be poured into a tissue site and will flow to fill and conform to the tissue site. The particles are substantially spherical and have a radius between about 1 mm and 5 mm. The tissue matrix particles each comprise a plurality of tissue matrix fragments having a length between about 5 μm and 300 μm, wherein the tissue matrix fragments are joined to one another to form the tissue matrix particles.

In certain embodiments, the tissue products produced as described herein provide improved properties when implanted or during storage. For example, the products described herein may be less susceptible to damage caused during freezing than other acellular tissue matrices. In addition, the matrices may have an improved ability to allow cellular ingrowth and vascularization.

FIG. 1 illustrates a process for producing a tissue product according to various embodiments. As shown at step 101, the process begins with selecting a tissue matrix 100. Suitable tissue matrices are discussed further below, but the tissue matrices can include any substantially acellular tissue matrix produced from human or animal tissue, which retains the ability to support cellular ingrowth and tissue regeneration without excessive inflammation. Certain exemplary tissue matrices that may be used include STRATTICE™ and ALLODERM® (LIFECELL® Corporation, Branchburg, N.J.), which are porcine and human acellular dermal matrices, respectively. However, other suitable tissue matrices can be used, including, for example, small-intestine submucosa. In addition, the tissue matrices can include intact tissues (not decellularized) and/or tissues that have been partially decellularized and/or populated with exogenous cells.

Next, as shown at step 111, the matrix 100 is processed to produce fragments 110. The tissue fragments 110 can be formed using a range of sizes and different morphologies. For example, in some embodiments, the tissue fragments 110 are in the form of small strands or threads of tissue matrix that has been treated to produce the desired size distribution and/or shape. In various embodiments, the strands or threads have a length between about 5 μm and 300 μm, between about 50 μm and 200 μm, between about 50 μm and 300 μm, or any values in between. In certain embodiments, the strands are approximately 40 microns×140 microns to 100 microns by 350 microns.

The tissue fragments 110 can be produced using a variety of processes. For example, any suitable cutting, grinding, milling, blending, shearing, or other mechanical process can be used, which produces the desired size and shape and does not cause unsuitable damage or change to the tissue matrix. In certain embodiments, the tissue fragments 110 are processed using a mill such as a SYMPAK® food mill or a QUADRO Attrition Mill (Quadro, Canada). In some embodiments, the tissue matrix 100 is cut into small pieces (e.g., 4 cm×4 cm) and then milled. In addition, the matrix may be blended briefly in a solution (e.g., PBS) prior to milling.

In some cases, the tissue matrices 100 can be processed to produce the fragments 110 when wet or submerged in a liquid. For example, the tissue matrices 100 can be milled or otherwise processed when submerged in a buffer such as PBS or any other suitable buffer. Further, after processing, the buffer can be at least partially removed by centrifuging or filtering to remove some or all of the liquid component. For example, a suitable centrifugation protocol can include centrifuging at 4,500 rpms for about 60 min.

After processing to produce tissue fragments 110, groups of the fragments 120 are formed to produce particles 120 having a desired shape, as shown at Step 121. The specific shapes and sizes of the particles 120 can vary based on the intended implantation site, to control space between particles to provide channels for cellular and vascular ingrowth, or to control the ability of the particles to flow into a desired treatment site. The tissue particles 120 can be shaped using a variety of molding or shaping processes. For example, the fragments 110 may be placed into a mold and/or compressed, rolled into a desired shape, or otherwise manually manipulated to produce the desired shape.

In some embodiments, the particles can be formed by immersion in a cold liquid. For example, fragments containing a buffer such as PBS can be extruded from a syringe and slowly dropped into liquid nitrogen. The material, when dropped into liquid nitrogen will form small particles, and the relative dimensions of the particles can be controlled by controlling the speed of extrusion and water content of the materials.

In some cases, after extrusion, the materials can be further processed to produce a desired shape and/or structure. For example, in some cases, the frozen materials are placed into a mixing device, such as a panner. A panner is a cooking attachment to a mixer, which acts like a rock tumbler or cement mixer; it rotates at a given speed and tumbles whatever objects are inside to achieve a coating of whatever powder or liquid is added. However, other similar mixing devices can be used. After placement in the mixing device, additional dry strands produced as discussed above may be added to the mixing device (e.g., at approximately a 1:1 ratio of particles and dry strands). The materials, with or without the additional dry strands can be processed in the panner or similar mixing device to produce a more spherical shape, and or change the size of the particles]. Optionally, the particles may be at least partially dried while in the panner. For example, the frozen particles in the mixing device can be exposed to low levels of hot air (e.g., approximately 48° C. as a velocity that does not blow the particles out of the processing device). As the particles in the mixing device are slowly heated and dried, additional tissue fragments in the form of dry powder may be added to keep the particles coated. Adding the dry powder, in this way, can assist in pulling residual moisture to the surface of the particles to dry the interior. Optionally, the particles may be further dried within the mixing device to remove most moisture.

A variety of shapes can be used for the tissue particles 120. For example, the tissue particles 120 can be formed into substantially spherical shapes, oblong shapes (e.g., ovoid), cubes, rectangles, noodles, pyramids, or any other desired shape. In some embodiments, the shape is selected to control flowability when implanted. For example, spherical shapes may be selected to allow a high degree of flowability. Alternatively, more oblong shapes may be selected to allow filling of a space while preventing migration out of a desired location. In addition, the specific shape may be selected to control the space between particles. For example, a spherical shape and size may be selected to produce a certain amount of porosity to allow cellular ingrowth and/or formation of vascular or extracellular structures.

In addition, the size of the particles can be varied based on a desired application. For example, the particles may have a longest dimension between about 1 mm and about 5 mm. Therefore, if the particles are spherical, the particles will have a diameter between about 1 mm and 5 mm, and if the particles are ovoid, the particles will have a long axis with a length between about 1 mm and 5 mm.

In various embodiments, the particles are processed such that the fragments making up the particles are joined to one another to form stable structures, as shown at Step 131. In certain embodiments, the fragments are joined without the use of substantial amounts of binder or adhesives. In addition in some embodiments, the fragments are dried using a process that is believed to join the fragments without significant cross-linking. For example, in some cases, the fragments may have frayed ends that interlock with one another. Further, in some embodiments, the fragments may bind to one another by non-covalent binding. As discussed elsewhere, the particles may be dried using a process such as convective drying, and such processes can produce particles having fragments that are joined to one another.

In some embodiments, the fragments are joined to one another by cross-linking. Cross-linking can be accomplished using a number of processes such as dehydrothermal cross-linking, exposure to UV light, and/or chemical cross-linking. In some embodiments, a dehydrothermal cross-linking process is used to allow cross-linking while simultaneously drying the particles. In addition, using any of the cross-linking processes, the particles may be further dried (e.g., by freeze-drying or air drying) to remove additional moisture.

In various embodiments, the tissue products can be selected to have certain properties that facilitate implantation and tissue filling and/or regeneration. For example, in certain embodiments, the tissue particles are dry before implantation. The dry particles can form a flowable mass that will fill a void or pocket in a tissue site. The tissue particles can be dried by freeze-drying and/or concurrently with a dehydrothermal cross-linking process. In addition, in the particles can be selected such that they swell when contacted with an aqueous environment, as may be present in a tissue site. As such, the particles can expand when implanted to fill a selected tissue site.

In some embodiments, the particles are dried by convective heating. For example, frozen particles may be placed in a convection dryer (e.g., HARVEST Brand Kitchen Convection Dryer). Drying may be performed at approximately 45° C. However, lower or higher temperatures may be used, as long as temperatures that cause unacceptable denaturation or other tissue damage are not used. In addition, it should be noted, that even when partially or mostly dried, as described above using a panner, the particles may be further dried to remove excess moisture.

After drying, the particles are packaged and sterilized to form a final product 140, as shown at Step 141. The product can be package in a variety of known medical containers and can be sterilized using conventional processes as long as the processes do not damage the product (e.g., by excessive cross-linking) in an unacceptable manner. In some embodiments, the product can be packaged in foil-to-foil pouches and irradiated. In some embodiments, the product can be irradiated with e-beam radiation. Suitable e-beam doses can include 15-22 kGy or ranges therebetween.

The tissue products of the present disclosure can be used to treat a variety of different soft tissue or hard tissue sites. For example, the products can be used to replace, repair, regenerate or augment tissue lost or destroyed due to surgery, trauma, and/or any pathologic process. In some embodiments, the tissue products can be implanted in a soft tissue site such as a lumpectomy site. In other embodiments, the products can be used to treat or augment bone, muscle, subcutaneous tissue, and/or adipose tissue.

In certain embodiments, internal negative pressure can be applied within the tissue product. In certain embodiments, negative pressure can serve to draw cells from surrounding tissue into the implanted acellular tissue product, increasing the rate at which native cells migrate into the tissue product and enhancing the speed and/or overall effectiveness of tissue approximation.

In certain exemplary embodiments, internal negative pressure is delivered to the acellular tissue matrix by a reduced pressure therapy device. The reduced pressure therapy device can include a pump fluidly connected, e.g., through a fluid passage or tubing to the acellular tissue matrix, and which delivers reduced or negative pressure to the acellular tissue matrix. A variety of reduced pressure therapy devices can be used. For example, suitable reduced pressure therapy devices include V.A.C.® therapy devices produced by KCI (San Antonio, Tex.).

Acellular Tissue Matrices

The term “acellular tissue matrix,” as used herein, refers generally to any tissue matrix that is substantially free of cells and/or cellular components. Skin, parts of skin (e.g., dermis), and other tissues such as blood vessels, heart valves, fascia, cartilage, bone, and nerve connective tissue may be used to create acellular matrices within the scope of the present disclosure. Acellular tissue matrices can be tested or evaluated to determine if they are substantially free of cell and/or cellular components in a number of ways. For example, processed tissues can be inspected with light microscopy to determine if cells (live or dead) and/or cellular components remain. In addition, certain assays can be used to identify the presence of cells or cellular components. For example, DNA or other nucleic acid assays can be used to quantify remaining nuclear materials within the tissue matrices. Generally, the absence of remaining DNA or other nucleic acids will be indicative of complete decellularization (i.e., removal of cells and/or cellular components). Finally, other assays that identify cell-specific components (e.g., surface antigens) can be used to determine if the tissue matrices are acellular.

In general, the steps involved in the production of an acellular tissue matrix include harvesting the tissue from a donor (e.g., a human cadaver or animal source) and cell removal under conditions that preserve biological and structural function. In certain embodiments, the process includes chemical treatment to stabilize the tissue and avoid biochemical and structural degradation together with or before cell removal. In various embodiments, the stabilizing solution arrests and prevents osmotic, hypoxic, autolytic, and proteolytic degradation, protects against microbial contamination, and reduces mechanical damage that can occur with tissues that contain, for example, smooth muscle components (e.g., blood vessels). The stabilizing solution may contain an appropriate buffer, one or more antioxidants, one or more oncotic agents, one or more antibiotics, one or more protease inhibitors, and/or one or more smooth muscle relaxants.

The tissue is then placed in a decellularization solution to remove viable cells (e.g., epithelial cells, endothelial cells, smooth muscle cells, and fibroblasts) from the structural matrix without damaging the biological and structural integrity of the collagen matrix. The decellularization solution may contain an appropriate buffer, salt, an antibiotic, one or more detergents (e.g., TRITON X-100™, sodium deoxycholate, polyoxyethylene (20) sorbitan mono-oleate), one or more agents to prevent cross-linking, one or more protease inhibitors, and/or one or more enzymes. In some embodiments, the decellularization solution comprises 1% TRITON X-100™ in RPMI media with Gentamicin and 25 mM EDTA (ethylenediaminetetraacetic acid). In some embodiments, the tissue is incubated in the decellularization solution overnight at 37° C. with gentle shaking at 90 rpm. In certain embodiments, additional detergents may be used to remove fat from the tissue sample. For example, in some embodiments, 2% sodium deoxycholate is added to the decellularization solution.

After the decellularization process, the tissue sample is washed thoroughly with saline. In some exemplary embodiments, e.g., when xenogenic material is used, the decellularized tissue is then treated overnight at room temperature with a deoxyribonuclease (DNase) solution. In some embodiments, the tissue sample is treated with a DNase solution prepared in DNase buffer (20 mM HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid), 20 mM CaCl₂ and 20 mM MgCl₂). Optionally, an antibiotic solution (e.g., Gentamicin) may be added to the DNase solution. Any suitable buffer can be used as long as the buffer provides suitable DNase activity.

While an acellular tissue matrix may be made from one or more individuals of the same species as the recipient of the acellular tissue matrix graft, this is not necessarily the case. Thus, for example, an acellular tissue matrix may be made from porcine tissue and implanted in a human patient. Species that can serve as recipients of acellular tissue matrix and donors of tissues or organs for the production of the acellular tissue matrix include, without limitation, mammals, such as humans, nonhuman primates (e.g., monkeys, baboons, or chimpanzees), pigs, cows, horses, goats, sheep, dogs, cats, rabbits, guinea pigs, gerbils, hamsters, rats, or mice.

Elimination of the a-gal epitopes from the collagen-containing material may diminish the immune response against the collagen-containing material. The a-gal epitope is expressed in non-primate mammals and in New World monkeys (monkeys of South America) as well as on macromolecules such as proteoglycans of the extracellular components. U. Galili et al., J. Biol. Chem. 263: 17755 (1988). This epitope is absent in Old World primates (monkeys of Asia and Africa and apes) and humans, however. Id. Anti-gal antibodies are produced in humans and primates as a result of an immune response to a-gal epitope carbohydrate structures on gastrointestinal bacteria. U. Galili et al., Infect. Immun. 56: 1730 (1988); R. M. Hamadeh et al., J. Clin. Invest. 89: 1223 (1992).

Since non-primate mammals (e.g., pigs) produce a-gal epitopes, xenotransplantation of collagen-containing material from these mammals into primates often results in rejection because of primate anti-Gal binding to these epitopes on the collagen-containing material. The binding results in the destruction of the collagen-containing material by complement fixation and by antibody dependent cell cytotoxicity. U. Galili et al., Immunology Today 14: 480 (1993); M. Sandrin et al., Proc. Natl. Acad. Sci. USA 90: 11391 (1993); H. Good et al., Transplant. Proc. 24: 559 (1992); B. H. Collins et al., J. Immunol. 154: 5500 (1995). Furthermore, xenotransplantation results in major activation of the immune system to produce increased amounts of high affinity anti-gal antibodies. Accordingly, in some embodiments, when animals that produce α-gal epitopes are used as the tissue source, the substantial elimination of a-gal epitopes from cells and from extracellular components of the collagen-containing material, and the prevention of re-expression of cellular a-gal epitopes can diminish the immune response against the collagen-containing material associated with anti-gal antibody binding to a-gal epitopes.

To remove a-gal epitopes, after washing the tissue thoroughly with saline to remove the DNase solution, the tissue sample may be subjected to one or more enzymatic treatments to remove certain immunogenic antigens, if present in the sample. In some embodiments, the tissue sample may be treated with an α-galactosidase enzyme to eliminate a-gal epitopes if present in the tissue. In some embodiments, the tissue sample is treated with a-galactosidase at a concentration of 300 U/L prepared in 100 mM phosphate buffer at pH 6.0. In other embodiments, the concentration of a-galactosidase is increased to 400 U/L for adequate removal of the α-gal epitopes from the harvested tissue. Any suitable enzyme concentration and buffer can be used as long as sufficient removal of antigens is achieved.

Alternatively, rather than treating the tissue with enzymes, animals that have been genetically modified to lack one or more antigenic epitopes may be selected as the tissue source. For example, animals (e.g., pigs) that have been genetically engineered to lack the terminal a-galactose moiety can be selected as the tissue source. For descriptions of appropriate animals see co-pending U.S. application Ser. No. 10/896,594 and U.S. Pat. No. 6,166,288, the disclosures of which are incorporated herein by reference in their entirety. In addition, certain exemplary methods of processing tissues to produce acellular matrices with or without reduced amounts of or lacking alpha-1,3-galactose moieties, are described in Xu, Hui. et al., “A Porcine-Derived Acellular Dermal Scaffold that Supports Soft Tissue Regeneration: Removal of Terminal Galactose-α-(1,3)-Galactose and Retention of Matrix Structure,” Tissue Engineering, Vol. 15, 1-13 (2009), which is incorporated by reference in its entirety.

After the acellular tissue matrix is formed, histocompatible, viable cells may optionally be seeded in the acellular tissue matrix to produce a graft that may be further remodeled by the host. In some embodiments, histocompatible viable cells may be added to the matrices by standard in vitro cell co-culturing techniques prior to transplantation, or by in vivo repopulation following transplantation. In vivo repopulation can be by the recipient's own cells migrating into the acellular tissue matrix or by infusing or injecting cells obtained from the recipient or histocompatible cells from another donor into the acellular tissue matrix in situ. Various cell types can be used, including embryonic stem cells, adult stem cells (e.g. mesenchymal stem cells), and/or neuronal cells. In various embodiments, the cells can be directly applied to the inner portion of the acellular tissue matrix just before or after implantation. In certain embodiments, the cells can be placed within the acellular tissue matrix to be implanted, and cultured prior to implantation. 

What is claimed is:
 1. A tissue product, comprising: a plurality of dry tissue matrix particles comprising a longest dimension between about 1 mm and 5 mm, wherein the tissue matrix particles each comprise a plurality of tissue matrix fragments having a length between about 5 μm and 300 μm, and wherein the tissue matrix fragments are formed into the tissue matrix particles.
 2. The tissue product of claim 1, wherein forming the fragments into particles includes joining the fragments without use of a binder or adhesive.
 3. The tissue product of claim 2, wherein the fragments are joined by convective drying.
 4. The tissue product of claim 1, wherein the tissue fragments are cross-linked to one another.
 5. The tissue product of claim 1, wherein the tissue particles each have a length between about 2 mm and 3 mm.
 6. The tissue product of claim 4, wherein the tissue fragments are cross-linked to one another using a dehydrothermal crosslinking process.
 7. The tissue product of claim 1, wherein the particles are substantially spherical.
 8. The tissue product of claim 1, wherein the particles swell when contacted with water.
 9. The tissue product of claims 1, wherein the particles are flowable when dry.
 10. The tissue product of claim 1, wherein the particles form a porous structure with open channels between each of the particles that can support cellular ingrowth and vascularization.
 11. The tissue product of claim 1, wherein the tissue fragments are elongated strands of tissue matrix.
 12. The tissue product of claim 1, wherein the tissue matrix particles are dermal tissue matrix.
 13. The tissue product of claim 1, wherein the tissue matrix particles are porcine tissue matrix particles.
 14. The tissue product of claim 1, wherein the tissue matrix is an acellular tissue matrix.
 15. A method for producing a tissue composition, comprising: selecting a tissue matrix; treating the tissue matrix to produce fragments having a length between about 5 μm and 300 μm; forming the fragments into particles having a longest dimension between about 1 mm and about 5 mm.
 16. The method of claim 15, further comprising drying the particles to form a plurality of dry particles.
 17. The method of claim 15, wherein drying the particles includes subjecting the particles to a convective drying process.
 18. The method of claim 15, further including treating the particles with a dehydrothermal treatment process.
 19. The method of claim 15, wherein forming the fragments into a plurality of particles includes compressing groups of the fragments.
 20. The method of claim 15, wherein forming the fragments into a plurality of particles includes placing small groups of the fragments in a cold environment to freeze the groups.
 21. The method of claim 20, wherein placing small groups of the fragments in a cold environment to freeze the groups includes extruding the small groups into a cryogenic liquid.
 22. The method of claim 15, wherein the plurality of particles includes substantially spherical particles.
 23. The method of claim 15, wherein treating the tissue matrix to produce fragments includes milling the tissue matrix.
 24. The method of claim 15, wherein the fragments are strands of tissue matrix.
 25. The method of claim 15, wherein the tissue matrix is dermal tissue matrix.
 26. The method of claim 15, wherein the tissue matrix is porcine tissue matrix.
 27. The method of claim 15, wherein the particles are flowable.
 28. The method of claim 15, wherein the tissue matrix is an acellular tissue matrix. 